You cannot always assume 200kgs taxi out fuel. If you are planning a max take off mass, then if you burn less on taxi, you will officially be above max weight limitation. But if you are underfueled and you know you will burn less on taxi, then it is perfectly reasonable to specify any figure for taxi you may reasonably deem fit. It may help you avoid an unnecessary fuel uplift if you are down to minimum fuel. It's called 'fudging' again! Criticise me if you will, but accused of 'fudging' I put my hand up as 'guilty as charged!'. I have never once been criticised for it......apart from here on Pprune, by people who aren't sure of what they are talking about!